Composite metal bodies

ABSTRACT

Composite metal bodies are provided in which particles of at least one constituent are embodied in metal in which the constituent is normally insoluble or incompatible when the metal is in the molten state, e.g., graphite in aluminum, the composites being produced by melt processing.

United States Patent 11 1 1111 3,885,959

Badia et al. May 27, 1975 COMPOSITE METAL BODIES 1,750,751 3/1930 Geyer75/138 2,170,259 8/1939 Borofski et al. 75/135 [75] lnvemors- 'fRmgWOPd, 3,239,319 3/1966 P611610 29/1912 x Pmdeep Kumar Rohfltgb3,306,738 2/1967 Young et al. 75/148 x eth e 3,333,955 8/1967 wa11 6r etal. 75/148 x [73] Assigneez The International Nickel Company 3,551,14312/1970 Marukawa 6128.1. 75/148 x Inc., New York, NY.

[22] Filed: May 1971 Primary ExaminerL. Dewayne Rutledge 21 1 No 141,991Assistant ExaminerJ. M. Davis Attorney, Agent, or FirmEwan C. MacQueen;H Related US. Application Data 7 7 Raymond J Kenny [63]Continuation-impart of Ser. No. 715,937, March 25, 1968, abandoned,which is a continuation-in-part of Ser. No. 644,429, May 25, 1967,abandoned, which is a continuation-in-part of Ser. No. 585,097, Oct. 7,

1966, abandoned. [57] ABSTRACT [52] US. Cl. 75/138; 29/1912; 75/135;75/146; 75/l47 Composite metal bodies are provided in whlch part1- 51Int. Cl. (2226 21/00 C168 of least One Constituent are embodied in metal[58] Field of Search u 75/135 138 146 147; in which the constituent isnormally insoluble or in- 29/1912 compatible when the metal is in themolten state, e.g., graphite in aluminum, the composites being produced[56] References Cited by melt Processing- UNITED STATES PATENTS1,390,197 9/1921 Dower 75/135 X 21 Claims, 2 Drawing Figures FATENTEBMAY 2'! I975 FIG. 1

FIG. 2

COMPOSITE METAL BODIES This application is a continuation-impart of U.S.application Ser. No. 715,937, now abandoned filed Mar. 25, 1968, whichis a continuation-in-part of application Ser. No. 644,429, filed May 25,1967, now abandoned, which in turn is a continuation-in-part ofapplication Ser. No. 585,097, filed Oct. 7, 1966, now abandoned.

As is well recognized in the metallurgical art, various metals manifestany number of useful properties, properties enhanced by alloying withother constituents. Aluminum, for example, has many desirablecharacteristics, notably, light weight, resistance to various corrosivemedia and relatively high strength in relation to weight. However,aluminum surfaces are quite susceptible to surface damage such asgalling and scoring when subjected to sliding contact with otheraluminum surfaces.

The frictional characteristics of aluminum and known aluminum alloys aresuch that articles thereof cannot be used in self-mated sliding contactwithout maintaining therebetween a fluid film lubrication condition, acondition often impossible to maintain, particularly where contactpressures are high or sliding speeds are low. Therefore, where two sucharticles were to be used in self-sliding contact it has been necessaryfor most practical purposes to make one of the articles of a metal otherthan aluminum or to provide an interposing metal therebetween. Forexample, the skirts of aluminum pistons used in aluminum cylinder blockshave been plated with iron, chromium or tin or an iron liner has beenprovided in the cylinder.

In accordance herewith, however, the frictional shortcomings of aluminumcan be appreciably minimized by incorporating therein certainpercentages of graphite. These constituents are generally consideredmetallurgically incompatible in the sense that when graphitic carbon ismixed with molten aluminum it is rejected from the melt. In any case,using metal processing (pyrometallurgy), no such alloy, insofar as weare aware, has been produced on a commercial scale which contained anappreciable amount of graphite, say, 0.5, 0.6 percent, or more, andwhich significantly affected the frictional characteristics of thealuminum. Actually, the more recent attempts have been generallydirected to powder metallurgical techniques but such are unsatisfactoryin many instances for various reasons.

While the foregoing is directed to the aluminumgraphite metallurgicalsystem, other incompatible systems in which one constituent is insolubleas a practical matter in a molten bath of a second are clearlycontemplated. For example, zinc and magnesium are characterized bymetallurgical incompatibility with graphitic carbon and it would bedesirable to obtain lubricity and machinability benefits of graphite asa dispersoid in these metals. Illustrative of other incompatibleenvironments are silicon carbide in nonferrous metals, e.g., aluminum,zinc or copper; diamond in metals such as aluminum and zinc; mica insuch incompatible low melting point metals as zinc, lead, aluminum andmagnesium; heavy oxides in lead; silica, magnesia, alumina and otheroxides in metals such as copper and nickel; silica, magnesia and othersin aluminum; etc.

Accordingly, it is an object of the invention to provide alloys havingimproved characteristics, the alloys having dispersed substantiallythroughout a constituent (dispersoid) normally incompatible with thebase metal when the latter is in the molten condition.

A particular object is to provide aluminum alloy products characterizedby improved resistance to scoring, galling and/or seizure when used insliding contact against aluminum alloys under conditions of poorlubrication.

Other objects and advantages will become apparent from the followingdescription taken in conjunction with the accompanying drawing in which:

FIGS. 1 and 2 are reproductions of photomicrographs (magnificationdiameters), of etched sections of an aluminum alloy casting inaccordance with the invention.

Generally speaking, the present invention contemplates compositecompositions of 'matter comprised 'of particles of at least oneconstituent (dispersoid), e.g., graphite, distributed substantiallyuniformly throughout a solidified (cast) matrix of metal in which theconstituent is, as a practical matter, normally insoluble when thematrix metal is in the molten condition, e.g., metal from the groupconsisting of aluminum, magnesium and zinc in the case of graphite, theconstituent particles upon being introduced into and dispersed within amolten bath of such metal being characterized by coatings effective toimpart compositional stability to the molten bath. The percentage ofdispersoid so embodied should be at least 0.5 percent and up to not morethan about 15 or 20 percent by volume, a range of 1.5 or 2 to 5 or 10percent being deemed quite satisfactory for numerous applications. Morethan one such dispersoid can be present and other elements can beincorporated as necessary.

Incompatible systems include those in which a constituent is insolublein alloys as well as the base metals which might form the alloys. Inrespect of graphitic aluminum, for example, this includes not only purealuminum but alloys containing, in weight per cent, in addition to amajor proportion of aluminum, up to about 25% silicon, up to about 25%tin, up to about 15% copper, up to about 15% magnesium, up to about 20%zinc, up to about 10% nickel, up to about 8% cobalt, up to about 5%manganese, up to about 1% chromium and up to about 1.5% iron. Suchalloys preferably contain at least 5%, e.g., at least 8%, silicon topromote uniform distribution of graphite in the melt and to avoiddetrimental graphite segregation during solidification. For goodtoughness and wear resistance, from 5 to 16 percent,.say, 8 to 13percent, silicon is beneficial. However, the silicon should becontrolled in relation to any nickel so that the total percentagethereof does not exceed about 20 percent in order to avoidembrittlement. Small amounts of optional elements, e.g., titanium,boron, zirconium, vanadium, antimony and cadmium, may be included forpurposes such as grain refinement, strengthening, raising therecrystallization temperature, improving weldability, etc.

Further with respect to graphitic aluminum, in obtaining particularlygood results it has been found that at least about 1 percent of graphiteby volume (0.6 percent by weight) should be present, advantageously atleast about 1.9 or 2 percent by volume (about 1.2 percent by weight),for satisfactory frictional characteristics under conditions of poorlubrication, such as the mixed film condition where the fluid filmpartially breaks, and to be sildably operable to a substantial extent inthe boundary lubrication region. For toughness and good fluidity, thegraphite content should be not greater than about 7.8 or 8 percent byvolume (about 5 percent or slightly above by weight). A preferred alloycontains about 1.9 to about 7.8 percent (by volume) graphitic carbonand, by weight, about 4 to about 7 percent nickel, about 8 to about 13percent silicon, up to 4 percent, e.g., 0.5 to 4 percent, copper, up to1.2 percent, e.g., 0.3 to 1.2 percent, magnesium, up to 0.6% iron, thebalance essentially aluminum, the alloy possessing in the chill castcondition, gall and heat resistant characteristics particularly wellsuited for sliding contact elements in internal combustion engines,e.g., pistons.

With reference to graphitic alloys generally, beneficial improvements infrictional and/or machinability characteristics of metals such as zincand magnesium as well as aluminum are obtainable with graphite inamounts of at least 0.2 percent by weight, and upwards to 5, or even to'15 percent by weight in these metals. While improvement is obtainablewith as little as 0.05 percent graphite, the characteristics of suchalloys are greatly less desirable. Accordingly, it is of considerablebenefit to have substantially greater amounts of graphite,advantageously at least 0.6 or 1.8 percent, dispersed throughout thematrix metal.

In carrying the invention into practice, the constituent particles aremost advantageously metal coated when dispersed in a melt. And in thisconnection, the surface coatings are essentially metal, i.e., are in themetallic condition characterized by being essentially uncombined metaland essentially devoid of oxides or other compounds. The coatings becomeat least partially dissolved in the molten bath and can ultimatelyimpart useful characteristics. Beneficially, the alloys are chill cast,e.g., permanent mold cast or die cast, or are similarly rapidlysolidified such as in continuous casting.

In striving for the maximum percentage of retained dispersoid particlesin the melt and final product based upon the amount of particles added,the coatings should be completely continuous over the entire surface ofeach particle. While, for practical purposes, the coatings need not beentirely perfect, it is to be emphasized that the particles must besubstantially surrounded by the coatings, e.g., coatings over at least80 or 90 percent, advantageously 95 percent, of the surface of theparticle.

In formulating alloy compositions, the amount and nature of coatingmetal is taken into account. For example, should the coating be nickel,up to 10 percent, e.g., 0.05 to 10 percent thereof, can be added inproducing graphitic aluminum alloys since at least a goodly portionmelts, dissolves or is otherwise incorporated into the alloy, e.g., as anickel aluminide, and provides, especially in amounts of at least 4percent, e.g., 4 to 7 percent, hardness, strength and wear resistance atroom and elevated temperatures, and high retention and uniformdistribution of the graphite.

For the purpose of giving those skilled in the art a betterunderstanding of the invention the following illustrative examples aregiven:

To illustrate the importance of having at least about 1 percent byvolume (0.6 percent by weight) and most desirably at least 2.8 percentby volume 1.8 percent by weight) of graphitic carbon in an aluminum-basein accordance herewith, a series of alloys (Alloys l12 Table I) werechill cast and wear tested using a Hohman tester.

Alloy Preparation The alloys were prepared using nickel-coated graphiteparticles introduced into baths in a stream of nitrogen gas while thebaths were maintained at a temperature of about 1,400F. Average particlesizes (U.S. series and including coating) are also given in Table I.

The particles were introduced at a positive pressure of 2 psi from afeeder assembly comprised of a gas pressurized hopper with a valve atthe bottom for regulating flow, a steel tube connected to the valve exitand leading downward from the hopper, and a graphite nozzle attached atthe lower end of the tube. Nitrogen was provided from a pressurizedcylinder connected to the assembly by two conduits, one leading from thecylinder into the hopper, thereby pressurizing the hopper, and thesecond leading into the steel tube below the hopper. The weight ofparticles introduced was about 10 percent of the initial weight of thebaths and dispersion and retention of the particles in the bath metalswere satisfactory. The melts were cast at a pouring temperature of aboutl,400F. into iron chill molds and subsequent metallographic examinationconfirmed that the castings contained a great number of graphiteparticles dispersed uniformly throughout the matrix.

In preparing alloys 2 through 6, 9, 11 and 12, the nickel coatings wereabout 2 microns average thickness, whereas for 7, 8 and 10 the coatingswere about 15, 50 and 30 microns, respectively. The extent, if any, towhich the coatings remained on the particles of Alloys l to 12 could notbe determined. Optical and electron micrographic examination did notdisclose any nickel coating around the graphite particles in thesolidified alloys.

TABLE I Allo C Ni Cu Si Mg Fe Al Graphite No. Size 1 1.80 6.3 2.4 8.1 l0.23 Bal. 2 1.88 5.4 2.7 12.4 1 0.28 Bal. 80 3 1.42 4.9 2.4 9.8 l 0.88Bal. 80 4 0.66 4.24 0.47 9.9 0.3 0.61 Bal. 60 5 0.72 5.14 0.43 10.0 0.30.66 Bal. 6 0.26 4.6 2.6 7.8 l 0.26 Bal. 80 7 0.55 4.19 0.47 10.6 0.30.65 Bal. 200 8 0.26 5.14 0.43 9.2 0.3 0.63 Bal. 200 9 0.1 1 4.25 0.489.9 0.3 0.60 Bal. 40 10 0.08 4.72 0.46 9.9 0.3 0.66 Bal. 400 11* 0.9 6.00.5 11.5 0.4 0.6 Bal. 40 12* 1.12 2.0 0.5 11.5 0.4 0.6 Bal. 40

C(%) Graphitic Carbon; Bal. Balance Essentially *Nominal compositionexcept for graphitic carbon content.

Graphite Size The numeral 60 refers to particles which passed through a200 mesh screen (opening about 74 microns) but retained by a 325 meshscreen (opening about 44 microns) and is thus a representativeapproximate average of the largest and smallest of such particles. Theother sizes were determined in a similar manner.

Test Procedure and Results gether reached a maximum level of 2,480 psi.When the maximum bearing pressure was reached, the rotational speed wasdecreased (without decreasing the load) in steps until rotation ceaseddue to binding or else, if galling did not occur, until the heat andfriction increased to about the limiting capacity of the test apparatus.

A bearing parameter, B ZN/P, where Z is the oil viscosity incentipoises, N is the rotation speed in rpm. and P is the pressure inpsi at the mating surface, was used as an index of lubricationconditions at the mating surfaces. Inasmuch as the pressure increasesand viscosity and speed decrease during test, the specimens weresubjected to progressively deteriorating lubricating conditions.

One characteristic evaluated was resistance to seizure (due to galling)under conditions of poor lubrication, e.g., mixed lubrication orboundary lubrication, conditions where some breakdown of the lubricatingoil film occurs. Alloys which did not seize at relatively low bearingparameters are characterized by good galling resistance superior to thatof alloys which seized at relatively high bearing parameters.

As a further part of the overall wear test, the maximum coefficient offriction at which sliding contact operation was successfully maintained,i.e., the maximum coefficient of friction prior to seizure (if seizureoccurred) was determined. High maximum friction coefficients (Max. Mu)show good frictional characteristics and vice versa. In general, wherecoefficients of 0.07 or greater were obtained, the alloys weresatisfactory under boundary lubrication. If less than 0.07, the alloysfailed to reach a boundary lubrication condition characterized by abearing parameter not greater than 3.0 and could be operated only inmixed or full film lubrication.

Results of the l-Iohman tests are set forth in Table II. Except forAlloys 2 and 3, the bearing shoes were made from chill castings of analloy which is commercially used in cast cylinder blocks for internalcombustion engines and nominally contains about 12% silicon, less than0.005% carbon with the balance being aluminum. As to Alloys 2 and 3, theshoes were made of the same alloy as the rotating disc. The lubricatingoil for the aluminum-silicon alloy shoes was a No. 50 oil having aviscosity of 29 centipoises at 100F. and the oil for the self-matedtests was a No. 60 oil having a viscosity of 60 centipoises at 100F. Thenumbers in the columns average Max. Mu and Average Min. B in Table 11show the average values of the highest friction coefficients and thelowest values of the bearing parameter, respectively, that were reachedat the finish of each test.

Table II, reflects that Alloys 1 through 5, which contained at least0.6% graphite by weight (at least about 1% by volume), were operable upto and into boundary lubrication conditions characterized by acombination of a high coefficient of friction of at least 0.07 and a lowbearing parameter not greater than 3.0. Alloys 1 and 2, containing atleast 1.8 percent (about 2.8 percent by volume) graphite were slidablyoperable and resisted galling and seizure under severe boundarylubrication conditions characterized by very high friction coefficientsof at least about 0.09 in combination with very low bearing parametersnot exceeding about 1.5. In contrast, alloys which did not contain asmuch as 0.6 percent graphite all failed to resist galling and seizurewhen subjected to lubrication conditions which were not as severe as theboundary lubrication conditions endured by Alloys 1 through 5.

Hohman tests of greater severity, wherein the bearing load was increasedto a maximum of about 3,000 psi, were performed with specimens of Alloys11 and 12 mated against aluminum-silicon alloy shoes and using Aturbrio50 oil. Both alloys operated successfully into the boundary lubricationregion and resisted galling until very low bearing parameters of 0.75with Alloy l l and 0.47 with Alloy 12 were reached, the maximumcoefficients of friction obtained at galling being 0.1 10 and 0.099,respectively.

Uniform dispersion of graphite particles in accordance with theinvention are illustrated in FIGS. 1 and 2 by microstructures from a7-inch long, 2 inchdiameter chill cast bar of Alloy 3 cast in thevertical position. FIG. 1 was taken from a section of the bar which wasnear the top during casting and solidification, FIG. 2 being taken fromnear the bottom. Accordingly, microstructures from the same casting atcross sections separated by a vertical distance of about 6 inches showthat the graphite particles remained uniformly dispersed and did notdetrimentally segregate. FIGS. 1 and 2 also reflect the effectiveness ofthe nickel coatings in imparting compositional stability to the moltenalloy.

Nickel-coated graphite particles were also successfully injected into amolten bath containing about 6.5% tin, the balance essentially aluminum.Metallographic examination showed a high recovery of uniformlydistributed graphite. And, coppercoated graphite parti cles copper andabout 25% graphite) were successfully used in connection with analuminum-base melt containing about 11.5% silicon, less than 0.005%carbon, about 0.6% iron, about 0.5% copper and about 0.3% magnesium.Particle size ranged from about 75 to microns and the weight of theinjected powder was about 10 percent of the initial melt weight. Theparticles were dispersed satisfactorily, the alloy containing 4.7%copper and 0.69% graphitic carbon.

Nickel-coated graphite particles comprising about 75% nickel were alsoinjected into a melt containing about 4% aluminum and balanceessentially zinc. Microexamination showed a high recovery and uniformdistribution of graphite. Using optical and electron micrographicequipment the nickel coating was not observed around the graphiteparticles. By chemical analysis the alloy contained 1.15% graphiticcarbon, 3.25% nickel and 4.16% aluminum. Similarly, metal-coatedgraphite particles can be used in conjunction with other known zincalloys including those containing up to about 30% aluminum, up to about4% copper, up to about 0.4% lead, up to about 0.3% cadmium, up to about0.5% magnesium, balance essentially zinc.

Graphitic magnesium alloys containing 0.05 percent or more graphite canalso be produced in accordance with the invention. Such alloys cancontain up to 10% aluminum, up to 6% zinc, up to 4% rare earth metals,up to 3.3% thorium and up to 0.75% zirconium.

As exemplary of composites utilizing dispersoids other than graphite,highly satisfactory results have been obtained with both alumina andsilicon-carbide in each of aluminum, an aluminum-base alloy containingabout 12% silicon and a zinc-base alloy containing about 4% aluminum,and also with silica in the same aluminum-base and zinc-base alloys.About 3percent by weight of dispersoid powder (nickel coated) was addedto the aluminum and aluminum 12% silicon alloy, about 2% being added tothe zinc 4% aluminum alloy. The data is reported in Table III in respectof chill cast specimens.

The abrasion resistance of the above alloys was deemed to be extremelygood owing to the fact that these materials resisted cutting with steelblades and machining with carbide tool bits. For example, in order tomachine aluminum tensile bars containing the silicon carbide and aluminaparticles it was necessary to resort to diamond cutting tools. This isconsidered rather remarkable. It might also be added that copper-coatedand zinc-coated silica particles resulted in good composites.

In terms of specific articles of manufacture, good compositionalstability was achieved with chill casting fourteen automotive pistonsfrom a melt of molten graphitic aluminum (nickel coating used). Moltenmetal for each piston was tapped and hand ladled to the mold as aseparate operation, with stirring or skimming before each tap, so thatthe period while the metal was held in the furnace, tapped, ladled andcast covered about 40 minutes. The alloy was a commercial type nominallycontaining 9.5% silicon, 3.5% copper, 1% magnesium, the balance beingaluminum. Chemical analysis of the pistons reflected that each containedat least 1.25% graphite by weight. Using a conventional permanent mold,an aluminum piston containing 3.89% graphite has been successfully castand thereafter readily machined without difficulty.

Graphitic aluminum castings made by the process of the invention havealso been induction melted, stirred and recast without excessive loss ofgraphite, thereby demonstrating that for commercial purposes, masteralloys or scrap castings, gates, risers, etc., can be used as meltingstock for making graphitic aluminum cast articles and other products.This was unexpected and it is considered that this data indicates that aportion of the coating metal may remain or can remain intimatelyassociated with a goodly percentage of the dispersed particles, say, 5or 10 percent or more thereof, in the original solidified cast compositestate whereby the wetted condition is retained upon re-melting. Goodcompositional and microstructural stability at room temperature andelevated temperatures is another favorable attribute of the alloy;

In producing the subject composites, it is of benefit to propel orotherwise force the coated particles into the molten baths in anon-reactive gas stream. Nitrogen, argon, helium and other non-reactivegases can be used.

Coatings, particularly metal, about 0.2 to about 50 microns thickapplied by known methods, including vapor or chemical deposition, aresatisfactory. Coating thickness should be at least about 2 microns toensure the particles are essentially covered, but to avoid an excess ofcoating the thickness is preferably not greater than about 5 microns.Metal coatings may comprise, nickel, copper, cobalt, iron aluminum orzinc and alloys thereof. Others that might be mentioned, and thisdepends, of course, upon what might be desired in the final product, aresilicon, tin, cadmium, antimony, chromium and tungsten.

Dispersoid particles are preferably at least about 40 microns in averagecross-section size, particularly in the case of graphite, although sizesdown to 10 or 5 microns or even finer can be used. Particle size shouldnot exceed about 200 microns since larger particles may tend tosegregate too rapidly. With respect to graphite particularly, especiallygood recovery and uniform dispersion obtains with an average size ofabout 40 or 60 to microns. In some exceptional instances, ifsolidification can be brought about very quickly after injection, e.g.,3 to about 30 seconds, satisfactory results can be obtained withparticles as large as 2,000 microns. Casting fluidity is benefited byhaving, at least in the case of graphite, particles of generallyequiaxed configurations, e.g., relatively spheroidal or lump-like, andnot acicular or flake-like.

As will be appreciated by those skilled in the art, in the selection ofthe two or more incompatible materials, the dispersoid constituentshould not be one which decomposes at the bath temperature. In additionto the incompatible systems enumerated hereinbefore, it is contemplatedthat the dispersoid can be selected from the group consisting of oxides,carbides, nitrides and borides. Molybdenum disulfide would be anothersuch constituent, particularly for lubricity qualities. Variousintermetallic compounds are also contemplated.

As to graphite specifically, molten bath metals other than aluminum,zinc, magnesium, etc., in which graphite is virtually insoluble includecopper and copperbase alloys, notably brass and bronze, lead alloys andtin alloys.

As a practical matter, in dealing with various incompatible systems thedensities of the respective incompatible constituents should, generallyspeaking, preferably be such that one does not exceed the other by afactor of about three; otherwise, there is the possibility ofencountering immediate or rapid segregation as by sinking or floating.This, of course, is by no means an absolute requirement. Advantageously,the difference in respective densities should not exceed a factor oftwo. Incompatible systems include those in which the mutual insolubilityobtains and there is non-reactivity at temperatures up to severalhundred degrees above the melting point of the dispersion medium.

The subject invention is particularly applicable in the production ofgraphitic and other alloys for sliding contact elements includingpistons, bearings, cylinder liners and blocks, sliding valves, internalcombustion engine rotors, electrical pick-up shoes, etc. The inventionis also applicable to the production of wrought articles including rods,bars, tubes, plates, etc., made by working cast, including continuouslycast, alloys contemplated herein. For example, a graphitic aluminumalloy containing 0.51% carbon and 4.1% nickel was hot forged, hotrolled, cold rolled into rod and thereafter cold drawn to produce wire.Furthermore, the graphitic alloys, particularly of aluminum, are usefulfor provid-' ing wear and/or gall resistant surface claddings oroverlays, e.g., welded overlays, on composite articles. Also, abrasionresistant articles, including dies and the like, can be produced toadvantage in accordance herewith.

Although the present invention has been described in conjunction withpreferred embodiments, it is to be understood that modifications andvariations may be resorted to without departing from the spirit andscope of the invention as those skilled in the art will readilyunderstand. Such modifications and variations are consid ered to bewithin the purview and scope of the invention and appended claims.

We claim:

1. A new and improved cast aluminum base alloy, said alloy containing atleast about 0.6 percent by weight of uncombined graphitic carbon in theform of graphite particles of at least about but not greater than about2,000 microns average cross-section size, about 5 to 25% silicon, up toabout 25% tin, up to about copper, up to about 15% magnesium, up toabout zinc, up to about 10% nickel with the proviso that when the nickelcontent is at least 4% the total percentage of nickel plus silicon doesnot exceed 20%, up to about 8% cobalt, up to about 5% manganese, up toabout 1.5% iron, up to about 1% chromium, and the balance essentiallyaluminum, said graphite particles having been introduced into a moltenbath of the aluminum-base alloy in the form of metal coated particles,the metal coating being effective to have imparted compositionalstability to the base alloy in the molten condition.

2. An alloy in accordance with claim 1 in which the graphite particlesare from about 40 microns to about 400 microns in average cross-sectionsize and the carbon content is present in an amount from about 1.8 toabout 5 percent.

3. As a new article of manufacture, a cast sliding contact element inaccordance with claim 1 in which the alloy contains 8 to 13% silicon,about 4to 7% nickel and about 0.6 to 5% graphitic carbon and wherein theparticles are from about 60 to 400 microns in average cross-section sizeand characterized by sliding contact operability when mated against analuminum surface under a boundary lubrication characterized by acoefficient of friction of at least 0.7 and a bearing parameter up toabout 3.0.

4. A new article of manufacture in accordance with claim 1 in which thecast sliding contact element is a piston.

5. A metal body in the solidified condition having dispersed therein atleast about 0.6 percent and up to about 5 percent by weight ofuncombined graphitic carbon particles of an average size of from about40 microns to about 400 microns, the particles being disposed throughouta matrix metal in which graphite is substantially insoluble in themolten condition and formed of an alloy predominantly of one metal fromthe group consisting of aluminum, magnesium and zinc, said metal bodybeing characterized by enhanced frictional characteristics over thefrictional characteristics of the matrix metal when substantially devoidof graphite, said graphite particles having been introduced into amolten bath of the aluminum-base alloy in the form of metal coatedparticles, the metal coating being effective to have impartedcompositional stability to the base alloy in the molten condition.

6. An alloy asset forth in claim 5 wherein the predominant metal iszinc.

7. A metal body in accordance with claim 5 and formed of analuminum-base alloy containing 0.6 to about 5 percent by weight ofgraphitic carbon in the form of graphite particles of about 40 micronsto about 2,000 microns average cross-section size, 0.05% to about 10%nickel, up to about 25% silicon provided that when th nicket content isat least 4% the total percentage of nickel plus silicon does not exceed20 percent, up to about 25% tin, up to about 15% copper, up to about 15%magnesium, up to about 20% zinc, up to about 5% manganese, up to about1.5% iron, up to about 1% chromium with the balance essentially aluminumand characterized by improved frictional characteristics includingresistance to galling and seizing under mixed lubrication conditions.

8. A composite metal body in the solidified condition and consistingessentially of particles of at least one dispersoid constituentdistributed substantially uniformly throughout a metal matrix in whichthe dispersoid is normally insoluble, the dispersoid particles beingpresent in an amount of at least 0.5 and up to about 20 percent byvolume, the dispersoid particles being of an average cross-section sizeof less than 400 microns and being in intimate association with acoating metal which substantially enveloped the particles to confercompositional stability between the particles and matrix metal when inthe molten state.

9. A composite metal body in accordance with claim 8 in which at leastone of the dispersoid constituents is graphite.

10. A composite metal body in accordance with claim 9 in which thematrix metal is from the group consisting of aluminum, aluminum alloys,zinc, zinc alloys, magnesium and magnesium alloys, the dispersoidparticles being of an average cross section size of not greater thanabout microns.

11. A composite metal body in accordance with claim 10 containing nickelin which the matrix metal is aluminum or an aluminum alloy.

12. A composite metal body in accordance with claim 8 in which thecoating metal is from the group consisting of nickel, copper, cobalt,iron, aluminum and zinc and alloys thereof.

13. A composite metal body in accordance with claim 8 in which thedispersoid constituent is selected from the group consisting of oxides,carbides, nitrides and borides.

14. A composite metal body in accordance with claim 13 in which thedispersoid constituent is selected claim 15 in which the constituentmaterial is alumina.

19. A composite metal body in accordance with claim 14 in which theconstituent particle constitutes from about 0.5 to about 15 percent byvolume of the composite.

20. A composite metal body in accordance with claim 19 in which theparticles are from about 5 to about 400 microns average cross-sectionsize.

21. As a new article of manufacture, on abrasion resistant productformed from a composite body in accordance with claim 15.

1. A NEW AND IMPROVED CAST ALUMINUM BASE ALLOY, SAID ALLOY CONTAINING ATLEAST ABOUT 0.6 PERCENT BY WEIGHT OF UNCOMBINED GRAPHITIC CARBON IN THEFORM OF GRAPHITE PARTICLES OF AT LEAST ABOUT 5 BUT NOT GREATER THANABOUT 2,00 MICRONS AVERAGE CROSS-SECTION SIZE, ABOUT 5 TO 25% SILICON,UP TO ABOUT 25% TIN, UP TO ABOUT 15% COPPER, UP TO ABOUT 15% MAGNESIUM,UP TO ABOUT 20% ZINC, UP TO ABOUT 10% NICKEL WITH THE PROVISO THAT WHENTHE NICKEL CONTENT IS AT LEAST 4% THE TOTAL PERCENTAGE OF NICKEL PULSSILICON DOES NOT EXCEED 20%, UP TO ABOUT 8% COBALT, UP TO ABOUT 5%MANGANESE, UP TO ABOUT 1.5% IRON, UP TO ABOUT 1% CHAROMIM, AND THEBALANCE ESSENTIALLY ALUMINUM, SAID GRAPHITE PARTICLES HAVING BEENINTRODUCED INTO A MOLTEN BATH OF THE ALUMINUM-BASE ALLOY IN THE FORM OFMETAL COATED PARTICLES, THE METAL COATING BEING EFFECTIVE TO HAVEIMPARTED COMPOSITIONAL STAVILITY TO THE BASE ALLOY IN THE MOLTENCONDITION.
 2. An alloy in accordance with claim 1 in which the graphiteparticles are from about 40 microns to about 400 microns in averagecross-section size and the carbon content is present in an amount fromabout 1.8 to about 5 percent.
 3. As a new article of manufacture, a castsliding contact element in accordance with claim 1 in which the alloycontains 8 to 13% silicon, about 4to 7% nickel and about 0.6 to 5%graphitic carbon and wherein the particles are from about 60 to 400microns in average cross-section size and characterized by slidingcontact operability when mated against an aluminum surface under aboundary lubrication characterized by a coefficient of friction of atleast 0.7 and a bearing parameter up to about 3.0.
 4. A new article ofmanufacture in accordance with claim 1 in which the cast sliding contactelement is a piston.
 5. A metal body in the solidified condition havingdispersed therein at least about 0.6 percent and up to about 5 percentby weight of uncombined graphitic carbon particles of an average size offrom about 40 microns to about 400 microns, the particles being disposedthroughout a matrix metal in which graphite is substantially insolublein the molten condition and formed of an alloy predominantly of onemetal from the group consisting of aluminum, magnesium and zinc, saidmetal body being characterized by enhanced frictional characteristicsover the frictional characteristics of the matrix metal whensubstantially devoid of graphite, said graphite particles having beenintroduced into a molten bath of the aluminum-base alloy in the form ofmetal coated particles, the metal coating being effective to haveimparted compositional stability to the base alloy in the moltencondition.
 6. An alloy as set forth in claim 5 wherein the predominantmetal is zinc.
 7. A metal body in accordance with claim 5 and formed ofan aluminum-base alloy containing 0.6 to about 5 percent by weight ofgraphitic carbon in the form of graphite particles of about 40 micronsto about 2,000 microns average cross-section size, 0.05% to about 10%nickel, up to about 25% silicon provided that when th nicket content isat least 4% the total percentage of nickel plus silicon does not exceed20 percent, up to about 25% tin, up to about 15% copper, up to about 15%magnesium, up to about 20% zinc, up to about 5% manganese, up to about1.5% iron, up to about 1% chromium with the balance essentially aluminumand characterized by improved frictional characteristics includingresistance to galling and seizing under mixed lubrication conditions. 8.A composite metal body in the solidified condition and consistingessentially of particles of at least one dispersoid constituentdistributed substantially uniformly throughout a metal matrix in whichthe dispersoid is normally insoluble, the dispersoid particles beingpresent in an amount of at least 0.5 and up to about 20 percent byvolume, the dispersoid particles being of an average cross-section sizeof less than 400 microns and being in intimate association with acoating metal which substantially enveloped the particles to confercompositional stability between the particles and matrix metal when inthe molten state.
 9. A composite metal body in accordance with claim 8in which at least one of the dispersoid constituents is graphite.
 10. Acomposite metal body in accordance with claim 9 in which the matrixmetal is from the group consisting of aluminum, aluminum alloys, zinc,zinc alloys, magnesium and magnesium alloys, the dispersoid particlesbeing of an average cross section size of not greater than about 120microns.
 11. A composite metal body in accordance With claim 10containing nickel in which the matrix metal is aluminum or an aluminumalloy.
 12. A composite metal body in accordance with claim 8 in whichthe coating metal is from the group consisting of nickel, copper,cobalt, iron, aluminum and zinc and alloys thereof.
 13. A compositemetal body in accordance with claim 8 in which the dispersoidconstituent is selected from the group consisting of oxides, carbides,nitrides and borides.
 14. A composite metal body in accordance withclaim 13 in which the dispersoid constituent is selected from the groupconsisting of silica, alumina and silicon carbide.
 15. A composite metalbody in accordance with claim 14 in which the matrix metal is selectedfrom the group consisting of aluminum, aluminum alloys, zinc and zincalloys.
 16. A composite metal body in accordance with claim 15 in whichthe constituent material is silicon carbide.
 17. The composite metalbody in accordance with claim 15 in which the constituent material issilica.
 18. A composite metal body in accordance with claim 15 in whichthe constituent material is alumina.
 19. A composite metal body inaccordance with claim 14 in which the constituent particle constitutesfrom about 0.5 to about 15 percent by volume of the composite.
 20. Acomposite metal body in accordance with claim 19 in which the particlesare from about 5 to about 400 microns average cross-section size.
 21. Asa new article of manufacture, on abrasion resistant product formed froma composite body in accordance with claim 15.